1. Field of the Invention
This invention relates to a colorimetric sensor which is arranged to measure the color of light.
2. Description of the Related Art
FIG. 1 of the accompanying drawings shows the conventional colorimetric sensor for measuring the color of light. In FIG. 1, a part 1 represents the red sensor of a photo-electric conversion element which is provided with an R filter for photo-electric converting the red component of light. A part 2 represents the green sensor of a photo-electric conversion element which is provided with a G filter for photo-electric converting the green component of light. A part 3 represents the blue sensor of a photo-electric conversion element which is provided with a B filter for photo-electric converting the blue component of light. The colorimetric sensor which is arranged in this manner measures the color of an incident light by detecting the red, green and blue components of the light. Further, the color sensors are set in optimum sizes according to their sensitivity values. The blue sensor which has a lower sensitivity is arranged in a relatively large size. The red and green sensors which have a higher sensitivity are arranged in a relatively small size. For example, in the case of FIG. 1, the sizes of the red (R), green (G) and blue (B) sensors are set in the ratio of R : G : B=1 : 1 : 2 as they are in the sensitivity ratio of R : G : B.congruent.1 : 1 : 1/2. FIG. 2 shows another example of the colorimetric sensor of the prior art which has been disclosed in U.S. Pat. No. 4,633,300. In this case, each of the color sensors is divided into a plurality of split pieces which are arranged to radially extend and spread from the center of the colorimetric sensor to the periphery thereof as shown in FIG. 2.
The colorimetric sensor of FIG. 1, however, has the following drawback: In case that a shadow arises, for example, at an upper right part which is as indicated by a broken line a-a' in FIG. 1, the quantity of light incident on the blue sensor 3 alone decreases. Then, in the output of the colorimetric sensor, the output of the blue sensor 3 alone decreases. As a result, the blue component is judged to be weaker than the actual intensity of the blue component of the incident light. Further, in the event of a shadow arising at an upper left part, the quantity of light incident on the red sensor 1 and the green sensor 2 deceases. Then, the outputs of the red and green sensors of the colorimetric sensor come to decrease. As a result, the red and green components are judged to be weaker than their actual intensity while the blue component is judged to be relatively stronger than its actual intensity.
The colorimetric sensor of FIG. 2 also has a similar drawback which is as follows: A shadow arising at a corner part causes an error of the output of the colorimetric sensor. When a shadow arises, for example, at an upper right part which is as indicated by a broken line a-a', the quantity of light incident on the blue and green sensors 3 and 2 decreases. The outputs of the blue and green sensors 3 and 2 of the colorimetric sensor then decrease. As a result, the red component of the incident light is misjudged to have a higher intensity than its actual intensity.
In cases where an uneven state arises in light due to a shadow or the like, some adverse effect of a corner part is conceivable in general. The colorimetric sensor of the prior art arranged as described above, however, produces an erroneous output when some part has no light while other parts have light due to a shadow formed on the colorimetric sensor.